The light sensitive properties of iodide compounds, e.g., lead iodide, have been studied. These materials have been prepared either by dry techniques such as vacuum deposition, or by wet chemical means precipitating the metal iodide from solutions of lead and iodide ions. U.S. Pat. No. 3,764,368 describes lead iodide films with no light sensitivity at room temperature and which work only at temperatures higher than 120.degree. C.; write-erase properties are not described for the films. H. Tolle et al in Applied Physics Letters, Vol. 26, No. 6, pages 349-351 (1975), state that the mechanism of image formation in lead iodide film is such that acceptable images can only be formed at about 180.degree. C. Attempts, with questionable results were made by them to sensitize the marking process by covering the PbI.sub.2 film with a pure silver layer and by mixing with organic polymers. The prior art does not disclose the formation of stable images on metal iodide films at room temperature either by light or electrical current and does not disclose the possibility of erasing and rewriting in such films. This has been a limitation on use of the metal iodide film technology, e.g., in the computer industry for computer print-out, display and plotting.